Biosphere-Atmosphere Gas Exchange & Atmospheric Chemistry Group
Keywords: Photochemical air pollution, atmospheric chemistry modeling, eddy covariance, ozone, BVOCs,
vegetation, seawater, evapotranspiration, micrometeorology
Emission of biogenic volatile organic compounds from sewater
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Warming effects on the emission of biogenic volatile organic compounds from seawater
We quantified the mixing ratios of a suite of volatile organic compounds (VOCs), including isoprene, dimethyl sulfide (DMS), acetone, acetaldehyde, and monoterpenes, at a mixed natural Mediterranean vegetation site ∼4 km from the southeastern tip of the Levantine Basin (Ramat Hanadiv), where the sea surface temperature maximizes and ultra-oligotrophic conditions prevail. The measurements were performed between July and October 2015 using a proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS).
Satellite images of the measurement site at Ramat Hanadiv Nature Park. Left: location of the measurement site (red dot). Right: a zoomed-in image of the surrounding area of the measurement site (red dot). Background imagery from © Google Earth.
Wind direction and back trajectory analysis, supported by the Model of Emissions of Gases and Aerosols from Nature (MEGAN v2.1) indicated a dominant contribution from the seawater for isoprene and DMS mixing ratios.
Our analyses further suggest a major contribution, at least for monoterpenes, from the seawater. The results indicate that the Levantine Basin greatly contributes to isoprene emissions, corresponding with mixing ratios of up to ∼9 ppbv several kilometers inland from the seashore, while isoprene emissions correlated with the air temperature. The DMS mixing ratios were 1 to 2 orders of magnitude lower than those measured in 1995 in the same area, suggesting a dramatic decrease in emissions due to changes in the species composition induced by the rise in the sea surface temperature.
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Isoprene and MBO* origins. (a) Scatter plot of m/z69 mixing ratios as a function of the (m/z 87) ∕ (m/z 69) ratio. Low and high ratios indicate a predominant contribution of MBO* and isoprene, respectively. The orange dots were measured during the daytime and the dark blue dots during the night. (b) Fraction of time for each wind sector for which (m/z 87) ∕ (m/z 69) was less than 13 %, as a proxy for isoprene.
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* other species, in addition to MBO , including methyl propyl ketone, pentanal and other C5H10O compounds, may contribute to the m/z 87 signal.
BVOC mixing ratios as a function of the contribution from each wind sector during the daytime. The radial dimension represents the fraction of time for each wind sector during which the mixing ratios were within a certain range, as specified in the color key.